[racket] closing tab in Unix?

[John Clements]

I feel as though the answer must be howlingly obvious, but I'm missing 
it somehow; how are UNIX-users supposed to close tabs without the mouse? 
After quite a bit of exploration I see that on the Mac, for instance, 
there are keybindings named "Close Tab"---but those aren't in the list 
of available keybindings under UNIX.

Am I missing something obvious?
Many thanks!

John

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